Implementing a Multilayer Perceptron from Scratch in C++: A Neural Network Without Any Machine Learning Frameworks

This article introduces the multilayer_perceptron project published by GibratDylan on GitHub (released on June 8, 2026). The project implements a Multilayer Perceptron (MLP) from scratch using modern C++, relying only on the Eigen library for linear algebra operations and completely avoiding mainstream machine learning frameworks like TensorFlow and PyTorch. Its core value lies in helping developers deeply understand the underlying mathematical principles and computation processes of neural networks, making it an excellent educational resource for learning deep learning.

In the field of deep learning, most developers rely on high-level frameworks to simplify development but lack a deep understanding of the underlying principles of neural networks. This project aims to demonstrate the complete construction process of a feedforward neural network through a framework-free implementation, helping learners grasp the internal working mechanisms of neural networks.

MLP is a classic feedforward neural network architecture consisting of an input layer (receiving raw features), hidden layers (feature transformation and abstraction), and an output layer (generating prediction results). Neurons in each layer are fully connected, with information flowing unidirectionally and no cyclic connections.

C++ was chosen for its fine-grained resource control and efficient execution; the Eigen library is used to simplify matrix operations (such as multiplication, transposition, and differentiation). Core components include: 1. Network architecture definition (number of layers, number of neurons, activation functions); 2. Forward propagation (linear transformation and activation from input → hidden → output); 3. Activation functions (Sigmoid, ReLU, Tanh, Softmax); 4. Backpropagation (gradient calculation using the chain rule); 5. Weight update (optimization algorithms like gradient descent). The training process covers data preprocessing, parameter initialization, iterative training (forward/backward/update), model evaluation, and hyperparameter tuning.

Educational value of scratch implementation: 1. Deep understanding of backpropagation (gradient propagation, causes of gradient vanishing/explosion, impact of activation functions); 2. Mastery of numerical computation details (numerical stability, regularization, optimizers, batch processing); 3. Gaining performance optimization experience (memory layout, parallelization, compiler optimization). Comparison with frameworks:

Feature	Scratch Implementation (C++)	TensorFlow/PyTorch
Learning Curve	Steep	Gentle
Execution Efficiency	High (after optimization)	High (underlying C++)
Flexibility	Fully controllable	Framework-limited
Development Speed	Slow	Fast
Debugging Difficulty	Requires self-implementation	Built-in tools
Educational Value	Extremely high	Moderate
It is recommended to use mature frameworks in production environments, but scratch implementation is the first choice for learning and research.

Applicable scenarios: Computer science students (course practice), algorithm engineers (understanding underlying principles), embedded developers (lightweight deployment), researchers (quick verification of new architectures). Extension directions: Convolutional Neural Networks (CNN), Recurrent Neural Networks (RNN), regularization techniques (Dropout, batch normalization), advanced optimizers (Adam), GPU acceleration, model serialization.

Practical suggestions: 1. First understand neural network theory; 2. Study the source code to understand the role of each function; 3. Use step-by-step debugging to track the propagation process; 4. Modify parameters for experiments; 5. Perform performance analysis to find bottlenecks; 6. Compare with framework results for verification. Summary: This project is an excellent educational tool. Although it lacks the convenience of production-level frameworks, it helps learners touch the essence of neural networks. A deep understanding of underlying principles is the foundation for making correct technical decisions and innovations.